Acute kidney injury after nephron sparing surgery and microwave ablation: focus on incidence, survival impact and prediction

Figures & data

Table 1. Characteristics of the study cohort before PSM.

Parameter	NSS (n = 1267)	MWA (n = 210)	p Value
Age (yr)	50.93 ± 13.36	62.96 ± 14.8	<0.0001^a
Gender			0.599^b
Male	966 (76%)	157 (75%)
Female	301 (24%)	53 (25%)
CCI score			<0.0001^b
0	369 (29%)	7 (3%)
1	286 (23%)	26 (12%)
2	232 (18%)	41 (20%)
3	204 (16%)	50 (24%)
4	107 (8%)	13 (6%)
5	42 (3%)	18 (9%)
6	14 (1%)	27 (13%)
7	5 (0.4%)	14 (7%)
8	4 (0.3%)	3 (1%)
9	4 (0.3%)	9 (4%)
10	0 (0%)	2 (1%)
Maximum diameter (cm)	2.41 ± 0.58	2.57 ± 0.84	0.105^b
Laterality			<0.0001^b
Left	660 (52%)	99 (47%)
Right	607 (48%)	111 (53%)
Pole			0.731^b
Upper pole	445 (35%)	60 (29%)
Middle-portion	332 (26%)	87 (41%)
Lower pole	490 (39%)	63 (30%)
Blood supply			0.544^b
Hypervascularity	1115 (88%)	193 (92%)
Hypovascularity	152 (12%)	17 (8%)
Adjacency			0.409^b
Safety	534 (42%)	117 (56%)
Intestine	289 (23%)	52 (24%)
Renal pelvis	444 (35%)	41 (20%)
Basic eGFR (mL/min/1.73 m^2)	97.71 ± 20.59	56.73 ± 28.48	<0.0001^a
Hemoglobin (g/L)	134.33 ± 20.74	136.62 ± 19.11	0.521^a
White blood cell (10^9/L)	6.12 ± 2.31	5.81 ± 2.48	0.133^a
Platelet (10^9/L)	197.47 ± 67.26	209.94 ± 60.81	0.176^a
ALT (U/L)	23.37 ± 26.77	22.69 ± 26.81	0.369^a
AST (U/L)	18.66 ± 12.22	19.63 ± 13.92	0.275^a
Albumin (g/L)	43.78 ± 7.61	40.34 ± 4.16	0.028^a
Total bilirubin (μmol/L)	11.57 ± 6.23	11.78 ± 5.72	0.619^a
Direct bilirubin (μmol/L)	3.57 ± 2.23	3.66 ± 2.11	0.597^a
Blood sugar (mmol/L)	4.76 ± 1.26	4.95 ± 0.98	0.312^a
Blood uric acid (μmol/L)	366.92 ± 92.86	357.40 ± 97.79	0.092^a
Total cholesterol (mmol/L)	4.37 ± 0.73	4.15 ± 0.30	0.225^a
Triglyceride (mmol/L)	1.34 ± 0.93	1.50 ± 0.84	0.121^a
Calcium (mmol/L)	2.29 ± 0.11	2.25 ± 0.10	0.788^a
Baseline eGFR category (%)			<0.0001^b
≥90	856 (67.59)	59 (27.83)
60–89	357 (28.15)	86 (40.57)
30–59	50 (3.94)	54 (25.47)
15–29	4 (0.32)	6 (2.83)
<15	0 (0)	7 (3.30)
Performance status			0.001^b
00	640 (50.5)	81 (38.5)
1	574 (45.3)	113 (53.8)
2	53 (4.2)	11 (5.2)
3	0 (0)	5 (2.5)
Renal score	5.56 ± 1.40	5.97 ± 1.13	0.457^a

Continuous variables are presented as mean ± SD or medians and interquartile ranges. Categorical variables are presented as no. (percentages within the columns).

^aStudent’s t-test.

^bPearson χ² test.

ALT = alanine transaminase; AST = aspartate aminotransferase; eGFR = estimated glomerular filtration rate.

Figure 1. Kaplan–Meier curve comparing CSS and OS between AKI and non-AKI patients. CSS: cancer specific survival; OS: overall survival.

Figure 2. Nomogram for the prediction of AKI after NSS or MWA, based on multivariable logistic regression analysis. Instructions: locate the patient's baseline eGFR on the corresponding axis. Draw a line straight downward to the score axis to determine how many points toward the probability of AKI the patient receives for his/her baseline eGFR. Repeat the process for each additional variable. Add the points for each of the predictors. Locate the final sum on the total score axis. Draw a line straight up to find the patient's probability of AKI. AKI = acute kidney injury; eGFR = estimated glomerular filtration rate; CCI = Charlson comorbidity index.

Table 2. Independent predictors of AKI.

Parameter	Single-variable logistic analysis		Multi-variable logistic analysis
	OR (95% CI)	p Value	OR (95% CI)	p Value
Blood supply
Hypovascularity	ref		ref
Hypervascularity	3.163 (1.378–7.263)	0.007**	3.091 (0.991–9.642)	0.052
Tumor diameter	2.326 (1.559–3.469)	<0.001**	3.084 (1.824–5.214)	<0.001**
CCI	1.905 (1.545–2.350)	<0.001**	2.133 (1.629–2.793)	<0.001**
Basic eGFR	0.951 (0.931–0.971)	<0.001**	0.94 (0.916–0.965)	<0.001**
Total cholesterol	1.134 (0.847–1.517)	0.399
Laterality
Left	ref
Right	0.964(0.569–1.632)	0.892
Pole
Lower	ref
Middle	0.695 (0.347–1.391)	0.304
Upper	1.029 (0.553–1.916)	0.928
Age	1.032 (1.008–1.057)	0.008**	0.999 (0.963–1.037)	0.978
Gender
Male	ref
Female	1.269 (0.738–2.179)	0.389
Adjacency
Safety	ref
Intestine	0.549 (0.245–1.231)	0.145
Renal pelvis	1.157 (0.433–3.096)	0.771
Procedure duration	0.999 (0.998–1.000)	0.173
Treatment modality
NSS	ref		ref
MWA	0.558 (0.326–0.954)	0.033*	0.598 (0.282–1.265)	0.178
Hemoglobin	1.002 (0.989–1.015)	0.802
White blood cell	0.976 (0.846–1.125)	0.734
Platelet	1.001 (0.997–1.006)	0.529
ALT	0.999 (0.988–1.011)	0.901
AST	0.995 (0.974–1.017)	0.668
Serum albumin	1.010 (0.946–1.079)	0.761
Total bilirubin	0.988 (0.945–1.033)	0.599
Direct bilirubin	0.949 (0.827–1.089)	0.454
Blood sugar	0.881 (0.677–1.147)	0.347
Blood uric acid	1.000 (0.997–1.003)	0.997
Triglyceride	0.886 (0.750–1.045)	0.151
Calcium	2.529 (0.202–31.654)	0.472
Blood loss	1.003 (1.000–1.005)	0.030*	1.001 (0.997–1.005)	0.509
RENAL Score	1.349 (1.119–1.628)	0.002**	1.302 (1.014–1.672)	0.039*
Performance status	3.027 (1.733–5.289)	<0.001**	1.145 (0.431–3.04)	0.786

Numbers in parentheses are the 95% CI.

*Data is significant statistical difference; *<0.05, **<0.01.

eGFR: estimated glomerular filtration rate; CCI: Charlson comorbidity index; ALT: alanine transaminase; AST: aspartate aminotransferase.

Figure 3. AUC, calibration curve and decision curve analysis of AKI nomogram. A, AKI nomogram ROC curve. The x-axis indicates 1-specificity and y-axis the sensitivity. Area under the curve of ROC (AUC = 0.864) represents the great AKI discriminative ability of the nomogram. B, AKI nomogram calibration curve. The x-axis represents the nomogram-predicted probability and y-axis AKI actual probability. A perfect prediction would correspond to the 45° blue dashed line. The red dotted line represents primary cohort (n = 316) and the black solid line is bias corrected by bootstrapping (B = 1000 repetitions), indicating observed nomogram performance. C, Decision curve analysis (DCA) of AKI nomogram. DCA demonstrating the net benefit associated with the use of the nomogram-derived probability, based on multivariable logistic regression analysis, for the prediction of AKI. AKI = acute kidney injury.

Table 3. Accuracy assessment of predictive OSP by Law of Total Probability.

Cohort	Actual OS	SP	Difference	t	p Value
NSS (n = 158)
Overall-year	0.947 ± 0.059	0.943 ± 0.062	0.004 ± 0.003	2.512	0.087
One-year	0.993 ± 0.005	0.993 ± 0.006
Three-year	0.982 ± 0.017	0.979 ± 0.020
Five-year	0.949 ± 0.031	0.944 ± 0.033
Seven-year	0.864 ± 0.035	0.856 ± 0.036
MWA (n = 158)
Overall-year	0.915 ± 0.078	0.914 ± 0.079	0.001 ± 0.001	2.611	0.080
One-year	0.993 ± 0.007	0.992 ± 0.008
Three-year	0.963 ± 0.015	0.963 ± 0.014
Five-year	0.881 ± 0.014	0.879 ± 0.015
Seven-year	0.822 ± 0.026	0.820 ± 0.028

Actual OS is the overall survival calculated by SPSS statistic software for 158 patients in NSS or MWA cohort. SP is the average value of overall survival probability predicted by Law of Total Probability for 158 Patients in NSS or MWA cohort.

SP = AKI risk × OS of AKI patients + (1 – AKI risk) × OS of non-AKI patients (OS of AKI patients and non-AKI patients were derived from the Kaplan-Meier analysis based on 158 patients in NSS or MWA cohort).

OS: overall survival; SP: overall survival probability; NSS: nephron sparing surgery; MWA: microwave ablation.